Difference in appearance between the two:
Color
Violet copper: usually has a purplish red color, which is the reason for its name. The color is more vivid and has a certain luster. As it oxidizes easily in the air, a dark red or dark black film of copper oxide may gradually form on its surface, but the overall purple-red background color can still be seen.
Oxygen-free copper: The appearance is generally a purer copper color, close to silver-white or light yellow. Because of the very low oxygen content, relatively stable in the air, the oxidation rate is much slower than the purple copper, so the surface color change is smaller, can be maintained for a longer period of time brighter metal color.
Surface Finish
Purple copper: Due to its relative softness, it is easy to appear scratches, scuff marks, etc. in the process of processing and use, and the surface finish may be affected to some extent. The oxidized surface of copper violet may appear rougher and lose part of its metallic luster.
Oxygen-free copper: usually has a higher surface finish, looks smoother and more delicate. Because of the high purity of oxygen-free copper, the material is relatively uniform, and it is easier to obtain a better surface quality in the processing.
Note: Distinguishing oxygen-free copper and copper violet through appearance is not an absolutely accurate method, because the appearance of copper may be affected by a variety of factors such as processing, surface treatment, oxidation and so on. In practice, if you need to distinguish accurately, you can also combine with other methods, such as chemical analysis, physical properties test, etc.
The difference in strength and hardness:
Purple copper: relatively low strength, hardness is also smaller, softer texture. This makes purple copper easy to deform during processing and use. For example, when making some thin-walled parts, the strength and hardness of purple copper need to be considered to avoid deformation or damage during use.
Oxygen-free copper: after special treatment, the strength is relatively high and the hardness is greater than that of copper violet. This makes oxygen-free copper more advantageous in some occasions that need to withstand certain pressure and wear and tear. For example, in the aerospace field, the high strength and hardness of oxygen-free copper can meet the stringent requirements for materials used in aircraft.
In terms of corrosion resistance, oxygen-free copper has better corrosion resistance than copper violet.
Difference in resistivity:
Violet copper: resistivity at 20°C is about 0.01851Ω-mm²/m (or 1.851×10-⁸Ω-m).
Purple copper has good electrical conductivity, second only to silver among all metals. However, its conductivity is slightly lower than that of oxygen-free copper. For example, in the electrical field, purple copper wire can transmit current better, but in some occasions where the conductivity is very high, it may not be able to meet the demand.
Oxygen-free copper: resistivity at 20°C is about 0.0171 μΩ-m (or 0.0171 × 10-⁶Ω-m).
Oxygen-free copper has a much higher electrical conductivity, generally up to 100% IACS (International Annealed Copper Standard) or more, much higher than that of copper violet. This gives oxygen-free copper a unique advantage in electronic and electrical fields. For example, in high-fidelity audio cables, oxygen-free copper can ensure high quality transmission of audio signals and reduce signal loss.
